Move winit logic from iced to iced_winit

- Added new `renderer::Windowed` trait. This shoud allow users to easily
  try different renderers by simply changing one line.
- Renamed `UserInterface` traits to `Application`, as the `run` method
  takes total control of the current thread.
- Moved `MouseCursor` back to `iced_native`. The new
  `renderer::Windowed` trait returns one on `draw`.
- Split `iced_native` renderer in multiple modules, for consistency.

native/src/lib.rs

@@ -206,6 +206,7 @@ mod element;
 mod event;
 mod hasher;
 mod layout;
+mod mouse_cursor;
 mod node;
 mod style;
 mod user_interface;
@@ -223,6 +224,7 @@ pub use element::Element;
 pub use event::Event;
 pub use hasher::Hasher;
 pub use layout::Layout;
+pub use mouse_cursor::MouseCursor;
 pub use node::Node;
 pub use renderer::Renderer;
 pub use style::Style;

native/src/mouse_cursor.rs

@@ -0,0 +1,35 @@
+/// The state of the mouse cursor.
+#[derive(Debug, Eq, PartialEq, Clone, Copy)]
+pub enum MouseCursor {
+    /// The cursor is out of the bounds of the user interface.
+    OutOfBounds,
+
+    /// The cursor is over a non-interactive widget.
+    Idle,
+
+    /// The cursor is over a clickable widget.
+    Pointer,
+
+    /// The cursor is over a busy widget.
+    Working,
+
+    /// The cursor is over a grabbable widget.
+    Grab,
+
+    /// The cursor is grabbing a widget.
+    Grabbing,
+}
+
+#[cfg(feature = "winit")]
+impl From<MouseCursor> for winit::window::CursorIcon {
+    fn from(mouse_cursor: MouseCursor) -> winit::window::CursorIcon {
+        match mouse_cursor {
+            MouseCursor::OutOfBounds => winit::window::CursorIcon::Default,
+            MouseCursor::Idle => winit::window::CursorIcon::Default,
+            MouseCursor::Pointer => winit::window::CursorIcon::Hand,
+            MouseCursor::Working => winit::window::CursorIcon::Progress,
+            MouseCursor::Grab => winit::window::CursorIcon::Grab,
+            MouseCursor::Grabbing => winit::window::CursorIcon::Grabbing,
+        }
+    }
+}

native/src/renderer.rs

@@ -1,8 +1,10 @@
 //! Write your own renderer.
 //!
-//! There is not a common entrypoint or trait for a __renderer__ in Iced.
-//! Instead, every [`Widget`] constrains its generic `Renderer` type as
-//! necessary.
+//! You will need to implement the `Renderer` trait first. It simply contains
+//! a `Primitive` associated type.
+//!
+//! There is no common trait to draw all the widgets. Instead, every [`Widget`]
+//! constrains its generic `Renderer` type as necessary.
 //!
 //! This approach is flexible and composable. For instance, the
 //! [`Text`] widget only needs a [`text::Renderer`] while a [`Checkbox`] widget
@@ -17,32 +19,13 @@
 //! [`text::Renderer`]: ../widget/text/trait.Renderer.html
 //! [`Checkbox`]: ../widget/checkbox/struct.Checkbox.html
 //! [`checkbox::Renderer`]: ../widget/checkbox/trait.Renderer.html
-use crate::{Color, Layout, Point, Widget};
+
+mod debugger;
+mod windowed;
+
+pub use debugger::Debugger;
+pub use windowed::Windowed;
 
 pub trait Renderer {
     type Primitive;
 }
-
-/// A renderer able to graphically explain a [`Layout`].
-///
-/// [`Layout`]: ../struct.Layout.html
-pub trait Debugger: Renderer {
-    /// Explains the [`Layout`] of an [`Element`] for debugging purposes.
-    ///
-    /// This will be called when [`Element::explain`] has been used. It should
-    /// _explain_ the given [`Layout`] graphically.
-    ///
-    /// A common approach consists in recursively rendering the bounds of the
-    /// [`Layout`] and its children.
-    ///
-    /// [`Layout`]: struct.Layout.html
-    /// [`Element`]: struct.Element.html
-    /// [`Element::explain`]: struct.Element.html#method.explain
-    fn explain<Message>(
-        &mut self,
-        widget: &dyn Widget<Message, Self>,
-        layout: Layout<'_>,
-        cursor_position: Point,
-        color: Color,
-    ) -> Self::Primitive;
-}

native/src/renderer/debugger.rs

@@ -0,0 +1,25 @@
+use crate::{Color, Layout, Point, Widget};
+
+/// A renderer able to graphically explain a [`Layout`].
+///
+/// [`Layout`]: ../struct.Layout.html
+pub trait Debugger: super::Renderer {
+    /// Explains the [`Layout`] of an [`Element`] for debugging purposes.
+    ///
+    /// This will be called when [`Element::explain`] has been used. It should
+    /// _explain_ the given [`Layout`] graphically.
+    ///
+    /// A common approach consists in recursively rendering the bounds of the
+    /// [`Layout`] and its children.
+    ///
+    /// [`Layout`]: struct.Layout.html
+    /// [`Element`]: struct.Element.html
+    /// [`Element::explain`]: struct.Element.html#method.explain
+    fn explain<Message>(
+        &mut self,
+        widget: &dyn Widget<Message, Self>,
+        layout: Layout<'_>,
+        cursor_position: Point,
+        color: Color,
+    ) -> Self::Primitive;
+}

native/src/renderer/windowed.rs

@@ -0,0 +1,17 @@
+use crate::MouseCursor;
+
+use raw_window_handle::HasRawWindowHandle;
+
+pub trait Windowed: super::Renderer {
+    type Target;
+
+    fn new<W: HasRawWindowHandle>(window: &W) -> Self;
+
+    fn target(&self, width: u16, height: u16) -> Self::Target;
+
+    fn draw(
+        &mut self,
+        target: &mut Self::Target,
+        primitive: &Self::Primitive,
+    ) -> MouseCursor;
+}